Bitterness, Pt. II

Phew! Where’s the time gone?

Anyway, let’s get on with it. I’ve already discussed the primary source of bitterness in beer, so now I’ll revisit the topic of bitterness from a different view: the physiology of bitterness.

The sensation of bitterness is not well understood at all. Nearly every aspect of bitterness is shrouded in complexity, and although new research is continually expanding our level of understanding there is still a great deal to be learned. The reasons bitterness is a tricky subject to elucidate are numerous and varied. There are a wide variety of chemical compounds which are bitter, such as polyphenols, organic acids, peptides, salts, sulfimides, and acyl sugars. This variety in molecular size and shape in turn implies a variety of mechanisms of operation. There is also a huge variation in how bitterness is perceived by individuals, and these variations are largely genetic in origin. Further confounding our understanding of these mechanisms are the difficulties that arise when attempting to communicate the qualities of bitter sensations. There are no agreed upon vocabularies for describing bitterness and its qualities, so while one person may describe caffeine as having a harsh and unpleasant bitterness another person may call it medicinal and lingering. Are they perceiving the same sensation, and is there even a way to tell for sure? Yet another factor in the complexity of bitter taste is the interactions that bitter sensations have with other sensations, most notably sweetness. Certain mixtures of bitter and sweet compounds can have interesting and unexpected effects on each other, with some sensations being suppressed by the presence of other compounds. In some cases there can be a synergistic effect where the total sensation is greater than what would be expected from a merely additive effect. In this article I will explain some of the mechanisms and characteristics of bitterness as we understand it so far.

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The IBU Assay

The spectrophotometer is among a small set of tools and equipment that are essential for a quality control lab to be adequately productive and accurate in a brewery setting. The reason for this is the BU assay which, apart from the HPLC, offers the best and most direct way to analytically measure the bitterness of beer that is available to brewers today. Relative to HPLC, the BU assay lacks precision, accuracy and sensitivity. But what makes it appealing are a number of things, foremost being the price: a couple thousand dollars can net you a new UV/Vis spectrophotometer and some supplies, whereas an HPLC can be an order of magnitude more expensive. Convenience, simplicity, and to some extent reliability are also among the benefits of this method, since HPLC, indeed chromatography in general, can be fickle and prone to error if rigorous procedures are not followed. Here, we’ll explore various aspects of the BU assay, including its origins and the fundamentals behind it.

20 things you “didn’t know” about taste.

Phil Plait (The Bad Astronomer) just tweeted a link to a fellow Discover Blog author’s post about 20 things that you didn’t know about taste. There’s a few interesting things in there, and they have lots of links to further information, but over half of those should already be known by anyone paying attention to semi-recent science news.

Jackpot! The Beer Fishbone Diagram

This PDF is a bonanza of information, enumerating the multitude of factors involved in all sorts of beer phenomena. It’s called a Fishbone Diagram, and the reason is obvious once you see it. I can’t even begin to explain everything that’s in here, I mean it would takes hours (days?) to pick it apart.

It’s pretty easy to interpret, although it is a bit of an information overload. Each page explains the various factors that influence a particular quality issue in beer. For example, below is a screenshot for the one of the pages [!] about how packaging and brewing issues interact to promote or limit beer oxidation. Other issues covered are controlling beer pH, fusel alcohols, H2S levels, foam quality, beer stability, yeast flocculation/vitality/viability, etc etc etc.

Brewing/Packaging Parameters and Beer Oxidation

You can find it here:
[see below]

Please excuse the rotated table of contents; I rotated the PDF so that the first page was the only one (of 42) that you needed to crane your neck to read. Better yet, print it out and enjoy it with a pint or two of your favorite beer. I’m going to go get a blonde ale out of the fridge right now.

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Edit, 1/6/11:  Looks like these fishbone diagrams were developed by Greg Casey, recently (currently?) of Coors Brewing.  I hope it’s OK that they’re posted here…

Edit, 1/2/13: I’ve recently been informed that the file on the host site disappeared, so I’ve rehosted it at another site. If it disappears again, shoot me an email and I’ll try to get it back up.

Edit, 1/23/13:  At the moment, the free file-hosting websites I’ve been using don’t seem to have much of a shelf-life.   Either that or Greg Casey has a Google Alert on “beer fishbone diagram” and every time he sees the file posted he submits a takedown request to the hosting site.

Anyway,  I’m going to do this on an on-demand basis.   If you’d like a copy of the Beer Fishbone Diagrams, email me (found on “About” page) and I’ll get you a copy within a couple days.  

Taste vs. Flavor: A retronasal excursion

So, when we talk about what a food or drink “tastes like”, it’s pretty common to get confused about the terminology.  You may hear someone say that something tastes “fruity” or “rancid” or whatever.  What they are actually discussing is how the food smells.  As we discussed already, “taste” applies only to the basic tastes. Everything else, apart from the various tactile sensations, is aroma. Combine the taste, the aroma, and the mouthfeel and you’re now talking about the overall flavor of the substance.

Here’s an exercise for you to try to drive home this point:

Eat or drink something while your nose is plugged.  What I like to use is a piece of gum or a mint candy or something. It might be tricky to swallow like this, but it’s possible.  So while your nose is plugged, what are you sensing?  Sweetness, sourness, saltiness, bitterness, temperature, texture, etc.  It’s all just taste and mouthfeel, right?  No aroma.    Now, unplug your nose and breath out through it.  NOW we’re in flavor country, eh? This aroma that you smell while food or drink is in your mouth is called “retronasal aroma” (backwards nose). It is distinct from “orthonasal aroma” (straight nose) which is sensed when you put your face over the food and smell normally through the front of the nose.

So apparently, the majority of food and beverage flavor is perceived by your nose.  What’s happening is, as the substance is in your mouth, it’s warming up.  This warming action allows the volatile aroma compounds to leave the food and enter the air in your mouth and sinus.  Also, the surface area of the food is increasing as you chew it and spread it around your mouth, which also allows more volatilization of flavors.  Other things might be happening as well, like bursting carbonation bubbles carrying even more flavors out of the beverage.  All these things are causing aromas to become “airborne” which allows them to be carried into your sinus (via the back of the mouth/throat). This retronasal method leads to distinct differences in the aroma of your food compared to the orthonasal method, since with the orthonasal method the warming and the agitation of the sample are considerably less. It’s not uncommon for the flavor profile of a food or beverage smelled retronasally to be quite unique from the same product smelled orthonasally, as certain compounds may not be volatile enough in the glass to be detected; they may need to be warmed and agitated to be detected at above-threshold levels. This demonstrates the importance of smelling AND tasting the product before you try to describe it.

Here is a diagram showing a cross-section of the human head, where you can see how the back of the throat is connected to the back of the sinus cavity.  This is where the retronasal aromas access the olfactory bulb at the top of the sinus (essentially the bottom of the brain) which houses the various receptors responsible for detecting aromas.

Cross section of mouth and sinus, showing how retronasal aromas access olfactory bulb.

So now that we understand how taste, aroma, and flavor are all related, we can use the correct terminology when we discuss our sensations and assess our beers with proper diligence.

Beer and our 5 senses

So, now that I’ve briefly introduced bitterness, I suppose I should step back and start with a more basic subject: how you use your 5 senses and the 5 basic tastes to enjoy beer.

The 5 Senses:

We all remember from grade school that the human body’s five senses are sight, sound, touch, smell, and taste. It’s fairly obvious that smell and taste play a part in experiencing beer, but what about the others?

Our eyesight comes from light in the visible range of the spectrum striking our retinas and exciting molecules which transmit a signal for our brain to interpret.  In beer, we notice the color, the clarity, the foam thickness, and the lacing in the glass.  All of these things are very important in building our impression of the beer.  It’s amazing how the color of the beer can bias the drinker before they’ve even tasted it.  I’ve seen taste panels ascribe caramel-like flavor descriptors to pale American lagers with caramel food coloring added to mask the true color.